<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>03_background-size</title>
    <style>
        div {
            width: 400px;
            height: 400px;
            padding: 50px;
            border: 50px dashed rgba(255, 0, 0, 0.7);
            /* background-image: url('../images/bg03.jpg'); */
            /* background-repeat: no-repeat; */

            /* background-size: 400px 400px; */
            /* background-size: 100% 100%; */
            /* background-size: contain; */
            background-size: cover;
        }
    </style>
</head>
<body>
    <div></div>
</body>
</html>